1. Field of the Invention
The invention relates to a method of fabricating an optical transformer, especially to a method that can simultaneously form an optical transformer and a metal interconnection system.
2. Description of the Prior Art
As technology progresses, semiconductor chips generated by a variety of semiconductor processes are pervasive in electronic devices, becoming necessaries in daily life. In addition to raising the integrity of semiconductor devices onto a chip so as to being smaller and compact, the current development trend also hopes to integrate various areas or fields of technology onto the semiconductor chip, enabling the chip to have different functions, for example, the combination of mechanical systems to be a micro-electrical system (MEMS), the combination of bio-technology to be a DNA chip, or the combination of optical fields to be an optical transmission system. Because the materials in various fields are of different physical nature, so the integration of those materials into existing manufacturing processes of semiconductor technology is an anxious problem to resolve.
Taking the optical transmission system for example, in order to convert the optical signal into existing semiconductor electrical signal, a variety of optical devices are needed, for instance, an optical waveguide, an optical transformer, an optical modulator, a photo-detector or other devices that are able to transmit, to separate, to combine optical signals, or to process electrical/optical switching. An optical transformer can receive outside optical signals and, by its special material or three-dimensional shape, can couple the signals into the optical waveguide. An optical waveguide can transmit the optical signals in conventional semiconductor medium and by using different materials of different refractive indices between the transmission medium and the coating medium, the light transmission integrity can be retained. Lastly, the optical signals are converted into a general electrical current message and provided to electronic devices for the subsequent signal processing.
Conventional optical transformers are usually formed in advance, and then each of the transformers is bonded onto the semiconductor substrate respectively. In detail, after forming the light waveguide, the already-formed light transformer is aligned and bonded onto the light waveguide by using an adhesive. However, the adhesive can easily contract when curing, and because of the different spreading effects due to different compositions of the adhesive, the coupling effect between the light waveguide and the light transformer will decrease, affecting its transmission quality. In addition, the current trend of development in optical transmission systems is to integrate it into the existing semiconductor substrate, such as a semiconductor substrate including a CMOS disposed therein. Therefore, effectively integrating the optical components and semiconductor components by using existing semiconductor technologies to form an optoelectronic structure on the substrate remains a problem to be solved.